2:00 PM InvitedRadiation Damage Tolerant Nanomaterials: Amit Misra1; 1Los Alamos National Laboratory An overview of the role of the structure and chemistry of interfaces in controlling the radiation damage tolerance of nanomaterials will be presented. A variety of interfaces in model systems were investigated via ion irradiation: grain boundaries in pure metals, and interphase boundaries in fcc-bcc metallic composites and metal-oxides and oxide-oxide composites.Helium ion implantation experiments were used to investigate the storage of stable nano-clusters of helium at interfaces, whereas helium as well as heavy ion irradiation experiments were used to study the evolution of radiation-induced-defect clusters in the vicinity of interfaces. The structural parameters of the interfaces are quantitatively correlated with the accumulation or removal of defects at interfaces. This research is funded by US DOE, Office of Basic Energy Sciences, Energy Frontier Research Center.

2:20 PM InvitedConsequences of Neutron Irradiation on ECAP Steel: Ahmad Alsabbagh1; Ruslan Valiev2; K.L Murty1; 1North Carolina State University; 2Ufa State Aviation Technical University Effects of neutron radiation exposure on microstructure and mechanical properties are examined on ultra-fine grained (UFG) carbon steel following equal channel angular processing. Corresponding studies are made on conventional grain (CG) sized material. Radiation hardening and embrittlement were noted in the conventional grain sized steel while relatively small changes were noted in UFG steel. In addition, grain size was noted to increase in the conventional grain sized steel in contrast to no significant effect in the UFG material. Work is in progress to investigate the radiation tolerance of UFG steel at higher fluences.Research is supported by ATR NSUF.

2:40 PM InvitedLaser-accelerated thin foil impact experiments for studies of intermetallic reactions in Nanolayered Ni+Al foils: Sean Kelly1; Naresh Thadhani1; 1Georgia Institute of Technology Shock-compression of fully-dense nano-Ni+Al multi-layered foils is investigated to probe the occurrence of shock-induced intermetallic-forming reactions. A laser-accelerated thin flyer impact system was utilized to determine the shock equation-of-state of the nano-layered Ni+Al foils. Measurements performed using time-resolved VISAR and PDV interferometry, showed evidence of shock-induced reaction based on change in the slope of the shock versus particle velocity response at pressures > 5 GPa, with recovered samples also clearly exhibiting a self-sustained reaction. Post-mortem high-resolution transmission electron microscopy (HRTEM) confirmed the formation of B2-NiAl in the reacted samples, and samples impacted at shock pressures below the reaction threshold revealed evidence of reactant mixing in regions close to heterogeneities associated with the wavy nature of the nano-layers. In this presentation, the mechanics of nano-layer deformation and strain localization at heterogeneities, leading to reaction initiation will be described.

3:00 PM The Surface Energy of the Al-Cu-Fe Quasicrystal: Jean-Marie Dubois1; 1Institut Jean Lamour Application niches for quasicrystalline thin films or coatings were pointed out in the areas of thermal insulation, infrared absorption, and reduced friction and adhesion, which led the author to be honored by the 2007 Mehl Award. Hence, attempts were made to estimate the surface energy (γS) of the stable i-Al62Cu25Fe13 (at.%) quasicrystal. Pin-on-disk experiments, after appropriate calibration, lead to reliable data in the range 0.5<γS<0.8Jm-2. Confirmation that γS lies in this range is provided by indirect measurements, based on the formation of composites made of blends of i-AlCuFe with immiscible metals like Sn and Bi. The average value of γS is about one half of that of pure aluminum (γS=1.15-1.2Jm-2), and less than a quarter of that of iron (γS=2.2-2.4Jm-2, consistently with the low wetting behavior and reduced friction coefficient observed for this quasicrystal. Correlation to specific features of the DOS will be emphasized.

3:20 PM Break

3:40 PM InvitedAtomic-scale Understanding of Deformation Twins in Hexagonal-close-packed Metals: Jian Wang1; Carlos Tome1; Irene Beyerlein1; John Hirth1; 1Los Alamos National Laboratory Deformation twinning/de-twinning, which are the dominant deformation mechanisms in hexagonal-close-packed (HCP) metals, exhibit more complex nucleation and propagation mechanisms than those associated with dislocation slip and those in cubic structures (FCC and BCC). Specifically, twinning and de-twinning are directional, involve atomistic shuffling, and they induce a strong crystallographic reorientation. Twin nucleation, a necessary first stage of twinning, seems to invariably take place at grain boundaries in hcp materials, and to involve complex dislocation reactions. After twin nucleates, propagation, growth, and interactions of twins seem more complicated than that in cubic crystals. In this talk, I will focus on the fundamental understanding of the aforementioned processes based on HRTEM observations and atomistic simulations. The fundamental mechanisms, including pure-shuffle, glide (shear)-shuffle and climb-shuffle, will be discussed in association with twinning and de-twinning.

4:00 PM CancelledDeformation Twinning and De-twinning in Nanostructured Materials: Xiaozhou Liao1; 1The University of Sydney Recent investigations indicated that increasing the density of twin boundaries can effectively strengthen materials and at the same time retain or improve their ductility because twin boundaries impede dislocation slip and also increase the dislocation storage capability in materials. Plastic deformation is a rapid and efficient way to produce a very high density of twins with twin boundary spacings in the nanometre regime in materials. In many situations, deformation can also lead to de-twinning. In this presentation, I will discuss our experimental observations of (1) the mechanisms of deformation twinning and de-twinning and (2) the effects of stacking fault energy, grain size and applied pressure on the twinning and de-twinning behavior in nanostructured materials.

4:20 PM InvitedSwitchable Deformation Mechanism in Columnar-grained Nanotwinned Metals: Zesheng You1; Xiaoyan Li2; Ting Zhu3; Huajian Gao2; Lei Lu1; 1Institute of Metal Research, CAS; 2School of Engineering, Brown University; 3Woodruff School of Mechanical Engineering, Georgia Institute and Technology Nano-scale twin strengthening represents a powerful strategy of achieving unprecedented mechanical properties (e.g., ultrahigh strength, high ductility, facile damage and flaw tolerance) in engineering metals and alloys. However, it has not been possible to tailor-design the nanostructures and associated properties in nano-twinned materials for obtaining targeted properties in a controlled manner. In this work, by integrating the nanostructure processing and characterization, we show that the strength and strain hardening properties can be tailored to vary over a large range in a columnar-grained nano-twinned copper simply by changing the loading orientations. We find such versatile performance can be achieved in a single nanostructured system owing to the switchable deformation mechanisms among different hard and soft modes of dislocation-mediated plasticity. Such switchable mechanisms are attributed to the unique layered organization of nanoscale twin lamellas in the columnar grains as well as the facile plastic shear mechanisms mediated by the coherent twin interfaces.

4:40 PM InvitedDeformation Twinning in Nano-scale Cu Layers: Rodney McCabe1; Irene Beyerlein1; John Carpenter1; Shijian Zheng1; Nathan Mara1; 1Los Alamos National Laboratory We examine twinning statistics in nano-layered Cu/Nb composites produced by accumulative roll bonding (ARB) using a novel, high spatial resolution electron backscatter (EBSD) technique. Below average layer thicknesses of 100 nm, twinning becomes an important deformation mode in the Cu layers. We reveal a significant orientation dependence, in which twinning is prevalent in Cu grains with certain orientations and rare for others despite similar strain histories and grain sizes. We develop a theoretical model that captures the favorability of twinning versus slip with crystal orientation. Interestingly, our results indicate that the size effects observed in nano-scale fcc metals are as much a consequence of crystal orientation and the large stresses as they are an inherent result of crystal size. We also quantify the effects of twinning on the evolving Cu texture and related interface characters present in the composites.

5:00 PM Basic Criteria for Formation of Growth Twins in High Stacking Fault Energy Metals: Xinghang Zhang1; Kaiyuan Yu; Daniel Bufford; Yue Liu; Youxing Chen; Haiyan Wang; 1Texas A&M University Nanotwinned metals received significant interest lately as twin boundaries may enable simultaneous enhancement of strength, ductility, thermal stability and radiation tolerance. However nanotwins have been the privilege of metals with low-to-intermediate stacking fault energy (SFE). Recent scattered studies show that nanotwins could be introduced into high stacking fault energy (SFE) metals, such as Al. In this talk we review several sputter-deposited (111) textured Ag/Al, Cu/Ni and Cu/Fe multilayers, wherein growth twins were observed in Ni, Al and face-centered cubic (fcc) Fe. The comparisons lead to important design criteria that dictate the introduction of growth twins in high SFE metals. The validity of these criteria was then examined in Ag/Ni multilayers.

5:20 PM The Influence of Stacking Fault Energy on the Formation of Highly Nanotwinned Cu-Al Alloys: Leonardo Velasco1; Mikhail Polyakov1; Andrea Hodge1; 1University of Southern California Thin films of pure Cu (99.999%) and Cu-Al alloys (Cu- 6 wt.% Al and Cu- 4 wt.% Al) were sputtered under identical conditions, in order to compare nanotwinned microstructures. Due to the wide range of stacking fault energies (SFE) in these materials (6-78 mJ/m2), the microstructure features were expected to change substantially. The temperature during processing was measured in order to explore and understand the different sputtering behavior for Cu and Cu-Al alloys and its influence on generating a nanotwinned structure. The samples produced were characterized by TEM and FIB. The Cu-Al samples showed highly columnar and nanotwinned structures, while the Cu samples presented few columnar grains, limited number of nanotwinned grains, and fine grain size. The reduced SFE of the Cu-Al alloys promoted a highly aligned nanotwinned columnar grain structure.